The invention is directed to an apparatus, for use with a standard automobile alternator, which selectively enables welding, operation of power tools, or conventional use of the alternator as the vehicle battery charger.
The invention is based on a simply modified motor vehicle alternator in which the output can be switched to either provide welding current, D.C. power suitable to operate power tools, or charging current for the vehicle battery (in the normal mode).
Prior art devices, such as U.S. Pat. No. 4,330,715 to Stroud et al and U.S. Pat. No. 4,599,687 to Smith have disclosed voltage doubling circuits connected to the windings of a modified motor vehicle alternator. These devices effectively increase the output voltage by employing large capacitors and power diodes, to a level sufficient to drive power tools, as well as by the use of switches to effect change from one operation mode to the other.
Smith employs a 3 phase two stage voltage doubling circuit using 6 large capacitors and 8 power diodes. The alternator regulator, however, is not a standard vehicle type, but rather is specially designed for the arrangement of the Smith device. Accordingly, should the Smith unit fail, there is no back up and the battery will either not charge or overcharge and suffer damage.
The Smith circuit is disadvantageous, because of its large number of hard wired power components, which results in a high manufacturing cost and high circuit complexity with the attendant associated increased risk of failure.
Another disadvantage of the Smith device is that the voltage multiplier is permanently connected to the alternator A.C. winding, even during normal running of the alternator. Since the Smith device is not isolated from the alternator the capacitors are kept charged while the vehicle is running. Thus, a failure in the Smith device during normal operation of the vehicle could result in vehicle failure.
A still further disadvantage of the Smith device is that it has no provision for regulating the welding voltage output.
Stroud et al employs a single stage voltage doubling circuit and similarly to Smith employs a non-standard voltage regulator. Although Stroud et al achieves a low component count, it does not supply sufficient power to drive 220 and 240 volt power tools due to the single stage doubling circuit.
Another disadvantage of the Stroud et al device is that it retains the welding socket connections 41 and 43 to the same points as the power socket R1. Connection of the appliance or power tool, during the welding mode, to the power socket could result in damage to the appliance due to low voltage.
A still further disadvantage of the Stroud et al device is that it has no provision for regulating the 110 volt output or the welding voltage output.
And finally, both the Smith and Stroud et al prior art devices are disadvantageous, because they fail to provide adequate safety and equipment protection circuits or devices.